1. Field of the Invention
This invention relates to an improved support for a susceptor on which is mounted a semiconductor wafer in apparatus used for the construction of integrated circuit structures on such wafers. More particularly, this invention relates to an improved support for a susceptor in a semiconductor wafer processing apparatus in which the outer edge of the susceptor is engaged by the support means, rather than the center of the susceptor, to provide more thermal uniformity across the susceptor, resulting in more even heating of the wafer.
2. Description of the Related Art
In the course of the forming of integrated circuit structures on semiconductor wafers, certain processes used involve the use of a heated susceptor or wafer support in an enclosed chamber, for example, during the growth of an epitaxial silicon layer, the formation of a thermal oxide or thermal nitride layer over silicon, or the rapid thermal annealing of integrated circuit structures already formed on the wafer.
As shown in the prior art structure of FIG. 1, a susceptor 2, on which is mounted a semiconductor wafer 16, is typically supported by a central support shaft 6 which may be either formed integrally with the susceptor or joined in some other manner to the center of the under surface of the susceptor, as seen in FIG. 1.
Typically, susceptor 2, and semiconductor wafer 16 mounted thereon, are located in a sealed processing chamber, such as the double domed chamber 10 shown in FIG. 1, where they are heated by a plurality of heating means 12 symmetrically arranged below susceptor 2 and chamber 10 in a housing 14, as well as over wafer 16 on susceptor 2 in chamber 10, as also shown in FIG. 1.
An apparatus showing, in more detail, such heating of the susceptor and the wafer is shown and claimed in Anderson et al. Ser. No. 07/491,416, filed Mar. 9, 1990 and assigned to the assignee of this invention, cross-reference to which is hereby made.
In that application, a series of heat lamps are circularly arranged below an inverted dome in which is mounted a susceptor on a central support shaft. Heat from the heat lamps radiates through the dome to the underside of the susceptor to heat the susceptor, as well as a wafer on the susceptor. The wafer is also heated by a second bank of heat lamps situated above another dome which is positioned over the wafer and susceptor.
The conventional use of a central support shaft in such an apparatus can result in uneven heat distribution along the susceptor, due to the thermal coupling of the central portion of the susceptor to the central support shaft, as well as the uneven distribution of the radiated heat from the heat source to the susceptor due to shadowing of the underside of the susceptor by the central support shaft. Such uneven heating, or thermal non-uniformity, of the susceptor can result in uneven heating of the wafer.
It would, therefore, be desirable to provide a support for a susceptor which would permit more even heating and thermal uniformity or heat distribution across the susceptor to provide more even heating of the semiconductor wafer being processed.